UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): June 30, 2003 Callisto Pharmaceuticals, Inc. (Exact name of registrant as specified in its charter) Delaware 333-63474 65-110840 (State or other jurisdiction (Commission (IRS Employer of incorporation or organization) File Number) Identification No.) 420 Lexington Avenue, Suite 601 New York, New York 10170 (Address of principal executive offices) Registrant's telephone number, including area code: (212) 672-9190 (Former name or former address, if changed since last report) Item 5 Other Events and Required FD Disclosure On June 30, 2003, Callisto Pharmaceuticals, Inc. announced the appointment of new members of the Board of Directors and certain management changes in connection with the merger agreement with Synergy Pharmaceuticals Inc. Item 7 - Financial Statements, Pro Forma Financial Information and Exhibits. (c) Exhibits Exhibit No. Description ----------- ----------- 99.1 Press Release of Callisto Pharmaceuticals, Inc. announcing appointment of new members of the Board of Directors and certain management changes in connection with the merger agreement with Synergy Pharmaceuticals Inc. 2 SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned, hereto duly authorized. Dated: July 1, 2003 CALLISTO PHARMACEUTICALS, INC. By: /s/ Gary S. Jacob ------------------------ Gary S. Jacob, Ph.D. Chief Executive Officer 3